Ink-jet printing mechanisms print images on a print medium by firing drops of ink from one or more pens while the pen moves back and forth across the print medium. An ink-jet printer is a device using such ink-jet printing mechanisms. Examples of ink-jet printers include plotters, facsimile machines, and typical computer-attached printers. The print medium on which a printer prints may be any sheet material, such as paper, MYLAR™, foils, transparencies, card stock, etc.
Ink-jet printers print dots by ejecting very small drops of ink onto the print medium. The printers typically include a movable carriage that supports one or more pens, each having a printhead with plural ink-ejecting nozzles. The carriage traverses the surface of the print medium, and the nozzles are directed to eject drops of ink at appropriate times pursuant to commands of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
Color ink-jet printers commonly employ a plurality of printheads which may be mounted on the carriage to produce different colors. Each printhead is connected to one or more reservoirs which contain ink for delivery to the printhead's nozzles. Typically, the reservoirs contain base colors such as cyan, magenta, yellow, and black. Depositing a drop of a base color ink produces a base-colored dot, while depositing multiple drops of different base color inks forms secondary or shaded colors. In other words, the base colors can be combined to form secondary or shaded colors.
Print quality is one of the most important considerations in the use of an ink-jet printer. Although the quality of an image generally is subjective, specific aspects of a printed image can be objectively identified as being indicative of poor print quality. For example, misaligned dots, missing dots, misshapen dots, small dots, large dots, and incorrectly colored dots all are objectively identifiable print errors. Those who are skilled in the art will understand and appreciate that a printed image is of poor print quality if the image exhibits one or more of the above-identified print errors. These errors typically arise from variations or tolerances in the various printing mechanisms or in the printer itself. In addition, various characteristics of the print media may affect print quality. Moreover, environmental conditions, such as temperature and humidity, may affect print quality.
Existing automatic techniques and systems for controlling print quality generally are based upon an estimate of how a specific action may affect print quality. These estimates lack verification of whether corrective action is actually necessary. Also, there is no reliable indication of the extent to which action should be taken to improve print quality. Further, known techniques for controlling print quality do not consider how a printed image actually looks, a factor which should be considered when addressing print quality.